1. Field of the Invention
This invention relates to a focal plane shutter and more particularly to a blade type focal plane shutter which is capable of travelling at a high speed.
2. Description of the Prior Art
To broaden the photographable region of a single-lens reflex camera, it is desirable to increase the maximum shutter speed and to provide a shutter speed synchronizable with a flash device. To meet this requirement, the shutter blind or blade speed must be increased. It is considered most effective, for that purpose, to reduce the weight of the shutter blades. However, merely lessening the thickness of the shutter blade for weight reduction would result in a blade with excessively lowered strength. Then, while travelling at a high speed, a slit forming blade would flex and collide with a partition plate which would be damaged thereby or would pop out from the shutter aperture. Furthermore, it has been difficult to develop a new material that has a small specific gravity and yet is strong enough for standing high speed travelling operations.
To solve this problem, it is conceivable to reinforce the shutter blinds or blades by providing them with embossed parts which increase their rigidity.
The conventional laterally travelling focal plane shutters of the roller blind type include shutters of the kind having thin metal blinds made of titanium foil or the like which are provided with many oblong embossed parts for preventing them from flexing during their travel as shown in FIG. 1 of the accompanying drawings. In a shutter of this kind, leading and trailing shutter blinds 51 and 52 just overlap slit forming ferrule parts 53 and 54 respectively while the embossed blinds do not overlap each other. This arrangement eliminates the possibility of light leakage from any gap that otherwise would arise between these ferrules 53 and 54 due to overlapping of these embossed blinds.
However, the structural arrangement of blinds and driving drums in the shutter of this kind inevitably has a large inertia. Compared with blade type shutters, therefore, shutters of this kind have the disadvantage of increasing the shutter blind speed. Hence, it has been known that, in order to increase the shutter speed, the shutter must be of the blade type.
However, with the blade type shutter, the blades overlap each other during shutter operation. Therefore, simply embossed shutter blades do not closely contact each other. The inadequate contact tends to cause light leakage. Besides, the embossed parts tend to be resistant or to stick during a shutter operation. Then, smooth operation of the shutter blades is hardly possible. In that event, the shutter blind speed cannot be increased and the exposure accuracy and the durability of the blades of the shutter are deceased. Therefore, that kind of shutter is not practical.
It is therefore an object of this invention to provide a blade type focal plane shutter which is capable of travelling at a high speed and yet excels in strength to eliminate the above-stated shortcomings of the prior art by virtue of an arrangement, wherein shutter blades and particularly the slit forming blade which has a large amount of kinetic energy are provided with embossed parts formed by subjecting a metal material, preferably such a light metal material as titanium, aluminum, magnesium, or the like, to a relatively simple drawing or molding process.
The above and further objects and features of this invention will become apparent from the following detailed description of preferred embodiments thereof taken in conjunction with the accompanying drawings.